This invention relates to the field of eyeglass frames and to a method of manufacturing a monolithic reinforced eyeglass frame employing a friction welding technique.
Eyeglass frames featuring a reinforcement element spanning the bridge portion of the frame are known from U.S. Pat. Nos. 1,428,697; 2,243,770; and 3,601,478. Currently, where it is desired to provide a reinforced eyeglass frame fabricated from a synthetic resin with the reinforcement member entirely embedded therein, the reinforcement number is sandwiched between two sheets of resin which are then bonded together with an adhesive. The resulting laminate is then machined, e.g., by routing, to provide a rough, or semi-finished, frame which is subsequently processed to provide the fully finished frame. This manufacturing technique results in a frame possessing a seam along the line where the resin sheets from which the frame is fabricated have been adhesively joined. Such a seam is undesirable from an aesthetic standpoint but, more importantly, is a potential site of structural weakness.
Friction welding is a known procedure for joining thermoplastic elements. In general, this technique involves frictionally heating the interface between the surfaces of the thermoplastic workpieces which are to be joined by applying contact pressure while at the same time rotating the workpieces relative to each other or imparting some other motion, e.g., an oscillating or linear reciprocating one, which will generate sufficient frictional heat to melt the thermoplastic at the interface. When such a molten state is achieved, the rotation or other frictional movement is discontinued while contact pressure is maintained until such time as the interface has solidified. The specific operational parameters selected are dependent in large measure on the nature of the thermoplastic materials involved, the configuration of the work pieces, the surface area of the interface, and so forth. Descriptions of various friction welding procedures and apparatus therefor can be found in U.S. Pat. Nos. 2,633,894; 3,970,491; 4,352,711; and 4,477,307 among others.
So far as is known, a monolithic reinforced eyeglass frame possessing a reinforcement member fully embedded therein has heretofore not been described. The term "monolithic" as used herein refers to a seamless reinforced eyeglass frame, i.e., one which appears to have been formed from, and structurally behaves as if it were in fact, a single sheet of thermoplastic material although in reality it is formed from adjacent thermoplastic sheets which have been friction welded together.